1. Field of the Invention
The present invention relates to graft copolymer compositions of various polymerizable monomers from poly(vinyl chloride) (PVC) obtained by living radical polymerization. It is postulated that the polymerization utilizes inherent structural defects present in PVC as the initiation sites for the polymerization reaction.
2. Description of the Prior Art
Graft and block copolymers have interesting properties due to the interaction between segments belonging to the same or different polymer molecules and have found many applications in the field of polymer chemistry and materials. Well defined grafting from poly(vinyl chloride) (PVC) has been limited, in the past, to ionic polymerization systems. For example see: Anionic Grafting Reactions, Gallot, Remp, Parrod, J. of Polymer Science 1, 329 (1975); Anionic Graft Copolymers. I. Poly(vinyl chloride)-g-Polystrene. Preparation and Characterization, Lechermeier, Pillot, Gole and Revillon, J. Applied Polymer Science, V. 19, pp. 1979-1987 (1975); Poly(vinyl chloride-g-Styrene): Synthesis, Characterization, and Physical Properties, Kennedy and Nakao, J. Macromol. Sci., A12(2), pp. 197-207 (1978). While these methods provide well-defined copolymers, the reaction conditions are characteristic for ionic polymerization in that they require very low temperatures and the absence of even traces of impurity such as oxygen, humidity and functional groups both in the reaction mixture and in the structure of the monomer.
Free radical polymerization has also been used to make graft copolymers of PVC. This was performed by initiation of the polymerization of the grafting monomer by a conventional radical initiator or by radiation. For example see: Studies on Grafting Glycidyl Methacrylate on Polyvinyl Chloride Backbone, Ravve, A., Khamis, J. T., J. Polym. Sci., 61, 185-194, 1962, Radiation Grafting of MMA onto PVC Films, Hegazy, El-Sayed. A.; Ebaid, A. R.; El-Sharabasy, S. A.; Mousa, A. M.; Hassan, A. Y., J. Appl. Polym. Sci., 41, pp. 2941-2950, (1990). These methods, however, produce a substantial amount of non-grafted homopolymer and non-soluble gel in addition to the grafted copolymer, which must be separated by fractionation of the product in order to have only grafted material.
Living polymerization is a process leading to formation of living polymers. Living polymers are able to grow whenever additional monomer is supplied. For example see: Szwarc, M. J. Polym. Sci.: Part A: Polym. Chem., 36, ix-xv, (1990). Formation of living polymers has many ramifications. Their average degree of polymerization is given by a simple relationship: Dpn=([M]oxe2x88x92[M])/[I] which increases linearly with conversion of monomer to polymer. The reaction is first order in monomer with a linear correlation between Ln([M]o/[M]) with time. Moreover, living polymerization leads to narrow polydispersity (Dpw/Dpn) of the formed living polymer, which decreases with conversion of monomer.
During the polymerization of vinyl chloride to PVC, in addition to regular xe2x80x94CH2 CHClxe2x80x94 repeat units, certain inherent structural xe2x80x98defectsxe2x80x99 are produced in the polymer which result in the PVC having xe2x80x98activexe2x80x99 or xe2x80x98labilexe2x80x99 chlorines. The presence of these structural defects has been extensively studied by different methods. For example see: Branch Structures in Poly(vinyl chloride) and the Mechanism of Chain Transfer to Monomer during Vinyl Chloride Polymerization, Starnes, Jr., Schilling, Plitz, Cais, Freed, Hartless and Bovey, Macromolecules, 16, pp 790-807 (1 983); Intramolecular Hydrogen Transfers in Vinyl Chloride Polymerization: Routes to Doubly Branched Structures and Internal Double Bonds, Starnes, Jr., Zaikov, Chung, Wojciechowski, Tran and Saylor, Macromolecules, 31, pp 1508-1517 (1998). Chlorine adjacent to double bonds (allylic chlorine) and chlorine on branched carbons (tertiary chlorine) are thought to be the most active or labile structural defects in the PVC.
Allyl halides have successfully initiated the metal-catalyzed living radical polymerization of styrene and methyl acrylate in the prior art, but this does not result in graft copolymers. For example see: Synthesis of Well-Defined Allyl End-Functionalized Polystyrene by Atom Transfer Radical Polymerization with an Allyl Halide Initiator, Nakagawa and Matyjaszewski, Polymer Journal, 30, pp138-141 (1998); How to Make Polymer Chains of Various Shapes, Compositions, and Functionalities by Atom Transfer Radical Polymerization, Gaynor and Matyjaszewski, ACS Symp. Ser., 685, pp 396-417 (1997); Synthesis of ABA Triblock Copolymers via a Tandem Ring-Opening Metathesis Polymerization: Atom Transfer Radical Polymerization Approach, Bielawski, C. W.; Morita, T.; Grubbs, R. H. Macromolecules, 33, 678, (2000).
Metal catalyzed living radical polymerization has been utilized for preparing polymers in general. For example see: Living Radical Polymerization of Styrene Initiated by Arenesulfonyl Chlorides and Cu1(bpy)nCl, Percec and Barboiu, Macromolecules, 28, pp 7970-7972 (1995); Metal-Catalyzed xe2x80x9cLivingxe2x80x9d Radical Polymerization of Styrene Initiated with Arenesulfonyl Chlorides. From Heterogeneous to Homogeneous Catalysis, Percec, Barboiu, Neumann, Ronda and Zhao, Macromolecules, 29, pp 3665-3668 (1996); DiSulfonyl Chlorides: A Universal Class of Initiators for Metal-Catalyzed xe2x80x9cLivingxe2x80x9d Diradical Polymerization of Styrene(s), Methacrylates and Acrylates, Percec, Kim and Barboiu, Macromolecules, 30, pp 6702-6705 (1997); Scope and Limitations of Functional Sulfonyl Chlorides as Initiators for Metal-Catalyzed xe2x80x9cLivingxe2x80x9d Radical Polymerization of Styrene and Methacrylates, Percec, Kim and Barboiu, Macromolecules, 30, pp. 8526-8528, (1 997); Arenesulfonyl Halides: A Universal Class of Functional Initiators for Metal-Catalyzed xe2x80x9cLivingxe2x80x9d Radical Polymerization of Styrene(s), Methacrylates, and Acrylates, Percec, Barboiu and Kim, J. Am. Chem. Soc., 120, pp. 305-316 (1998); Self-Regulated Phase Transfer of Cu2O/bpy, Cu(O)/bpy, and Cu2O/bpy Catalyzed xe2x80x9cLivingxe2x80x9d Radical Polymerization Initiated with Sulfonyl Chlorides. Percec, Barboiu and van der Sluis, Macromolecules, 31, pp. 4053-4056 (1998); Rate Enhancement by Carboxylate Salts in the CuCl, Cu2O and Cu(O) Catalyzed xe2x80x9cLivingxe2x80x9d Radical Polymerization of Butyl Methacrylate Initiated with Sulfonyl Chlorides, van der Sluis, Barboiu, Pesa and Percec, Macromolecules, 31, pp 9409-9412 (1998); Fluorocarbon-Ended Polymers: Metal Catalyzed Radical and Living Radical Polymerizations Initiated by Perfluoroalkylsulfonyl Halides, Feiring, Wonchoba, Davidson, Percec and Barboiu, J. Polym. Sci.: Part A: Polym. Chem., 38, pp 3313-3335 (2000); Transition-metal-catalyzed living-radical polymerization, Sawamoto and Kamigaito, Chemtech, 29, pp 30-38 (1999); Controlled/xe2x80x9cLivingxe2x80x9d Radical Polymerization. Atom Transfer Radical Polymerization in the Presence of Transition-Metal Complexes, Wang and Matyjaszewski, J. Am. Chem. Soc., 117, pp 5614-5615 (1995); Iniferter Concept and Living Radical Polymerization, Otsu, J. Polym. Sci. Part A: Polym. Chem., 38, 2121 (2000); From Telomerization to Living Radical Polymerization, Boutevin, J. Polym. Sci.: Part A: Polym. Chem., 38, 3235 (2000); and Highly Active Iron Imidazolylidene Catalysts for Atom Transfer Radical Polymerization, Louie and Grubbs, Chem. Commun., pp 1479-1480 (2000).
The use of a copolymer of vinyl chloride with vinyl chloro acetate to produce a graft copolymer by living radical polymerization has been described in Paik et. al., Macromol. Rapid Communications, 19, 47-52, (1998). Paik, et al teach that it is necessary to add active chlorine to the PVC by co-polymerization and the active chlorine from the vinyl chloro acetate is the initiator for the living radical graft co-polymerization. In the teaching of the instant invention, it is not necessary to undergo the difficult and expensive modification of the PVC in order to create active sites for the initiation of the living radical polymerization.
Similarly, living radical grafting from PVC has also been achieved via chemical modification of PVC by creating xanthane type initiation sites on the backbone of PVC, which act as an initiator. For example see: xe2x80x9cLivingxe2x80x9d Free Radical Graft Copolymers I: Preparation and Properties, Wang, H. T., Harwood, H. J., Sebenik A., Polymer Preprints, 34(2), 582-583, (1993). Creation of these initiation sites are difficult and expensive.
To overcome the deficiencies presented by ionic polymerization systems, it is proposed, in the instant invention, to utilize living radical polymerization systems. The instant living radical polymerization is accomplished by using reversible activation and deactivation of alkyl halides by transition metal complexes.
It has now been found that the allylic and tertiary chlorine (xe2x80x98active chlorinesxe2x80x99) normally found in PVC, in conjunction with certain transition metal catalysts, can successfully initiate the grafting of polymerizable monomers from the PVC backbone in a living fashion. Optionally, a solvent for the polymer and a ligand to help solubilize the metal catalyst can be utilized in the preparation of the graft copolymer composition of the present invention. These graft copolymers are useful as compatibilizers for blends and alloys, as high heat distortion temperature PVC materials, as permanently plasticized PVC materials, as impact modifiers, and in many other applications apparent to those skilled in the art.